1. Field of the Invention
The present invention relates to a high-energy ion implanter for fabricating a semiconductor device. More particularly, the present invention relates to a high-energy ion implanter, which is capable of detecting abnormal operating conditions of a turbo pump that provides a predetermined vacuum in a stripper, to implant an impurity into a wafer to fabricate a semiconductor device. The present invention prevents yield loss and wafer defects caused by abnormal operating conditions of the turbo pump.
2. Description of the Related Art
Conventionally, a semiconductor device is fabricated by performing several sequential processes, such as photolithography, ion implanting and diffusion, and etching to a wafer. The ion implanting process, one process in the fabrication of a semiconductor device, implants impurities as an ion type into a wafer, thereby providing a semiconductor device with a predetermined electric characteristic.
To ionize an impurity in the ion implanting process, it is necessary to provide a vacuum having a predetermined level. Accordingly, an ion implanter should be equipped with a turbo pump to provide vacuum conditions.
The ion implanter for implanting an impurity as an ion type into a wafer may be typically referred to as a medium current, a high current, or a high-energy ion implanter, according to usages and process conditions. Regardless of the type of ion implanter, however, the relevant principles are similar.
In other words, when the implanting ion accelerates ionized dopants to a wafer surface, the accelerated ion is implanted into a wafer. In this case, dopant amounts and ion implanting depth are closely related to atomic size, ion speed and duration of time the wafer is exposed to an ion implanting beam.
A high-energy ion implanter equips a large acceleration tube to a medium current ion implanter or, additionally, to a high-current ion implanter. Therefore, the size of a high-energy ion implanter is larger than that of any other conventional ion implanter. Additionally, a beam path thereof is long.
Referring to FIG. 1, a conventional high-energy ion implanter includes an ion source 100, a vaporizer cell 101, an analyzer magnet 102, a pre-accelerator 103, a tendetron accelerator 315, and a beam filter 108.
In operation, the ion source 100 generates positive ions from boron fluoride (BF3) gas, and the vaporizer cell 101 converts the positive ions from the ion source 100 into a desired polarity by utilizing magnesium (Mg). The analyzer magnet 102 separates a desired ion (i.e., a negative ion) from the polarized ions in the vaporizer cell 101. The pre-accelerator 103 applies a predetermined voltage to the separated ions (i.e., negative ions) from the analyzer magnet 102 and accelerates the separated ions by utilizing voltage differences.
The tendetron accelerator 315 includes a low-energy accelerator 104, a stripper 105, a high-energy accelerator 106 and a turbo pump 107. The low-energy accelerator 104 draws the ions from the pre-accelerator 103 and accelerates the ions for smooth polarity conversion. The stripper 105 eliminates electrons from the ions accelerated from the low-energy accelerator 104 in vacuum conditions by a stripping gas (e.g., nitrogen) to generate positive ions. Next, the high-energy accelerator 106 accelerates the positive ions generated from the stripper 105. The turbo pump 107 pumps the stripper 105 to provide vacuum conditions therein. The beam filter 108 filters the ion beam accelerated from the high-energy accelerator 106 of the tendetron accelerator 315 in an electrostatic state and implants the ion beam into a wafer transferred from a wafer transfer chamber 109.
The above described conventional high-energy ion implanter generates positive ions from the gas ionized in the ion source 100, wherein the ionized gas generated in the ion source 100 is sent to the vaporizer cell 101. The vaporizer cell 101 changes the polarity of the ions by utilizing magnesium (Mg) and the analyzer magnet 102 separates desired negative ions. More specifically, after initially accelerating the ions in desired energy states (e.g., 100 keV) through the pre-accelerator 103, the ions are accelerated again in the low-energy accelerator 104 of the tendetron accelerator.
The negative ions accelerated from the low-energy accelerator 104 are converted into positive ions, after the stripping gas (e.g., nitrogen) eliminates electrons in the vacuum conditions applied by the turbo pump 107. More particularly, the converted ions are accelerated again through the high-energy accelerator 106 and beam ions, which are filtered through the beam filter 108, are implanted into a wafer transferred from the wafer transfer chamber 109.
To implant positive ions into a wafer, the turbo pump 107 provides vacuum conditions in the stripper 105 for extracting positive ions only and for eliminating negative ions, by the stripping gas, from the ions accelerated from the low-energy accelerator 104. Referring to FIG. 2, another conventional high-energy ion implanter includes a turbo pump 107 including a circuit breaker 200 for supplying and interrupting power voltages applied from an outside source, a rotatable motor 201 for receiving the power voltages through the circuit breaker, a power transmission unit 205 for transmitting a rotational driving force from the motor 201 through a pulley 202, a belt 203, and a shaft 204, an electric generator 206 for generating predetermined voltages by the driving force transmitted from the power transmission unit 205, a central processing unit CPU 207 for driving the turbo pump 107, and a monitor 208 for displaying procedures by the CPU 207.
The rotational force from the motor 201, however, is often not normally transmitted to the turbo pump 107 and the generator 206 due to unstable conditions caused by vibrations of the pulley 202 in the power transmission unit 205, tension fluctuations of the belt 203, a broken shaft 204, or the like. Therefore, normal voltages, which are required to operate the pump smoothly and to provide desired vacuum conditions in the stripper 105, are not applied to the turbo pump 107 from the generator 206.
Accordingly, ions flowing in from the stripper 105 have inferior ion characteristics due to the abnormal vacuum conditions. Inferior ion characteristics are a cause of metal impurity generation and wafer defects while implanting the ions into a wafer.
Thus, when technical difficulties occur in the power transmission unit 205, the generator 206, or the turbo pump 107, the circuit breaker 200 interrupts the supply of the power voltages to cease operation of the turbo pump 107 and the generator 206. However, even though difficulties may occur in the turbo pump 107, the motor 201, the power transmission unit 205, or the generator 206, the conventional high-energy ion implanter may not be able to detect the abnormal operating conditions. Therefore, even though the generator 206 or the turbo pump 107 is not operating normally, the circuit breaker 200 does not perform the circuit interruption and continues to supply the AC power voltages to perform the ion implanting process.
As a result, the vacuum conditions in the stripper 105 are not normal due to abnormal operation of the turbo pump 107. The abnormal vacuum conditions generate the phenomena of the inferior ion characteristics, and result in yield losses due to an unsuccessful ion implanting process and due to metal impurities.
A feature of a preferred embodiment of the present invention is to provide a high-energy ion implanter capable of detecting abnormal operating conditions of a turbo pump for providing vacuum conditions in a stripper, while the stripper converts accelerated and flowed-in ions, to interrupt a circuit breaker. Therefore, an ion implanting process is suspended to prevent an unsuccessful ion implanting process and yield losses due to inferior ion characteristics.
In order to provide the above feature, a preferred embodiment of the present invention provides a high-energy ion implanter for fabricating a semiconductor device including a low-energy accelerator for converting a polarity of ions flowed in from an ion source; a stripper for converting the ions accelerated from the low-energy accelerator to positive ions in vacuum conditions; a high-energy accelerator for accelerating, in high-energy, the positive ions that are converted in the stripper; a turbo pump for providing vacuum conditions in the stripper; a current sensor for detecting currents to check for abnormal operating conditions of the turbo pump; and a central processing unit (CPU) that interrupts a circuit breaker to suspend the ion implanting process in response to the level of current detected in by current sensor.
Preferably, the current sensor is connected between the turbo pump and the circuit breaker to detect currents.
Preferably, the current sensor is a galvanometer for detecting minute currents.
These and other features of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.